Adaptive gas generators for an airbag are known in the prior art. Document EP 2 229 296 B1 describes an adaptive gas generator comprising two igniters which may be actuated independently of each other so that each of them define an amount of gas to be diffused into the airbag. As a counterpart, this gas generator notably has a complex internal architecture with mechanisms laid out in duplicate in order that each of them open discharge orifices of each pressurized gas reserve. The result of this is that the manufacturing cost with these numerous components is high on the one hand. On the other hand, it should be noted that these mechanisms are based on the principle of supporting a thin lid during the storage, and of suppressing this support in order to open the lid. Subsequently, the opening of the second lid may pose a problem if a portion of the gas has already escaped through the first orifice so that the residual pressure in the reserve is reduced, and the supporting force may not be sufficient for pushing the support and opening the lid.
An object of the present invention is to solve the drawbacks of the document of the prior art mentioned above and in particular, first of all, to propose a gas generator which has a simple and reliable opening mechanism, while providing the possibility of adapting the flow rate of gases diffused into the airbag.
For this, a first aspect of the invention relates to a gas generator for an airbag comprising:                a first reserve of pressurized gas with a first discharge orifice,        a second pressurized gas reserve with a second discharge orifice,        a first mechanism comprising a first actuator arranged for opening the first and second pressurized gas reserve,        a diffusion chamber arranged for diffusing towards the airbag the discharged gases through the first and the second discharge orifice,characterized in that the generator further comprises:        a mixing chamber in direct communication with the first discharge orifice and the second discharge orifice and comprising at least one first surface of communication with the diffusion chamber,        a second mechanism comprising a second actuator and a mobile obturator between a first obstruction position in which it obstructs a second surface of communication of the mixing chamber with the diffusion chamber and a second passage position in which the second communication surface is free, the second actuator being arranged for moving during its operation the mobile obturator from one of the first or second positions towards the other position.        